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Acetic and citric acids effect the type II secretion system and decrease the metabolic activities of salmon spoilage-related Rahnella aquatilis KM05
AbstractRahnella aquatilis causes seafoods to spoil by metabolizing sulfur-containing amino acids and/or proteins, producing H2S in products. The type II secretion system (T2SS) regulates the transport of proteases from the cytoplasm to the surrounding environment and promotes bacterial growth at low temperatures. To prevent premature fish spoilage, new solutions for inhibiting the T2SS of bacteria should be researched. In this study, global transcriptome sequencing was used to analyze the spoilage properties of R. aquatilis KM05. Two of the mapped genes/coding sequences (CDSs) were matched to the T2SS, namely, qspF and gspE, and four of the genes/CDSs, namely, ftsH, rseP, ptrA and pepN, were matched to metalloproteases or peptidases in R. aquatilis KM05. Subinhibitory concentrations of citric (18 µM) and acetic (41 µM) acids caused downregulation of T2SS-related genes (range from − 1.0 to -4.5) and genes involved in the proteolytic activities of bacteria (range from − 0.5 to -4.0). The proteolytic activities of R. aquatilis KM05 in vitro were reduced by an average of 40%. The in situ experiments showed the antimicrobial properties of citric and acetic acids against R. aquatilis KM05; the addition of an acidulant to salmon fillets limited microbial growth. Citric and acetic acids extend the shelf life of fish-based products and prevent food waste.
Global transcriptome analysis of Pseudomonas aeruginosa NT06 response to potassium chloride, sodium lactate, sodium citrate, and microaerophilic conditions in a fish ecosystem
Abstract Pseudomonas aeruginosa is an opportunistic pathogen that recently has been increasingly isolated from foods, especially from minimally processed fish-based products. Those are preserved by the addition of sodium chloride (NaCl) and packaging in a modified atmosphere. However, the current trends of minimizing NaCl content may result in an increased occurrence of P. aeruginosa. NaCl can be replaced with potassium chloride (KCl) or sodium salts of organic acids. Herein, we examined the antimicrobial effects of KCl, sodium lactate (NaL), sodium citrate (NaC), and sodium acetate (NaA) against P. aeruginosa NT06 isolated from fish. Transcriptome response of cells grown in medium imitating a fish product supplemented with KCl and KCl/NaL/NaC and maintained under microaerophilic conditions was analysed. Flow cytometry analysis showed that treatment with KCl and KCl/NaL/NaC resulted in changed metabolic activity of cells. In response to KCl and KCl/NaL/NaC treatment, genes related to cell maintenance, stress response, quorum sensing, virulence, efflux pump, and metabolism were differentially expressed. Collectively, our results provide an improved understanding of the response of P. aeruginosa to NaCl alternative compounds that can be implemented in fish-based products and encourage further exploration of the development of effective methods to protect foods against the P. aeruginosa, underestimate foodborne bacteria.